1. Field of the Invention
The present invention relates to an adjustable dose chamber. The invention has particular application to pneumatically powered tools.
2. Description of the Prior Art
Pneumatic drive systems are used in a variety of applications, particularly with regard to tools. Traditionally, pneumatic tools have been designed to be connected to a source of compressed air, such as a stationary air compressor.
While air compressors do provide an effectively unlimited supply of compressed air, they have several disadvantages. In particular, the need to connect a tool to the air compressor via a hose limits the portability of the tool and also the positions into which it can be manoeuvred. Additionally, air compressors are typically expensive and outside the financial means of some users. Further, safety issues arise from having the hoses lying around the work place which may become caught on various objects or trip up persons within the space.
In an attempt to address these problems, several different systems have been developed.
One such system utilises a combustible gas, such as butane, to provide an explosion that drives the tool's operation. Such combustion systems have safety issues of their own given that the tool usually includes a storage device for combustible gas and a combustion source close to each other. The gas and gas cartridges tend to be expensive and only available from select suppliers. Further, the heat and impact of the combustion tends to be hard wearing on the tool causing them to require frequent maintenance. The electrical components are very susceptible to failure if the tool is exposed to moisture such as rain. All of these factors add additional costs and an element of inconvenience to the user.
More recently, portable pressure sources have been developed by which a vessel containing a pressurised fluid such as carbon dioxide may be connected via a regulator to a tool traditionally powered by an air compressor. These systems allow the tools to be used in a more portable fashion without being restricted by the long hosing requirements of conventional set ups. However because the tools have been designed for a pneumatic set up where the supply of compressed air or gas is effectively unlimited, the energy transfer is relatively inefficient, particularly in the drive mechanism. Therefore, using these portable pressurised fluid systems generally results in the tool only being capable of achieving an impractically low number of repetitions before replacement or replenishment of the fluid vessel is required.
It would therefore be an advantage for the energy transfer mechanism of a pneumatic tool to be more efficient in terms of the consumption of gas per repetition.
Further, it would be advantageous to have the ability to easily adjust the quantity of gas consumed per repetition.
US Patent Application No. 2006/0107939 discloses an adjustable volume chamber for a compressed gas apparatus in the form of a paintball gun. The volume is adjusted by the translation of a sealed piston within the chamber. However if it was desired to adjust the volume of the chamber while pressurised, this adjustment would be against a significant amount of pressure. In a power tool application, the pressure of the system may be in the order of hundreds of psi, and very difficult to work against manually.
It would therefore be advantageous to have the ability to adjust the power of the tool while the system is pressurised.
All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.
It is acknowledged that the term ‘comprise’ may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term ‘comprise’ shall have an inclusive meaning—i.e. that it will be taken to an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term ‘comprised’ or ‘comprising’ is used in relation to one or more steps in a method or process.
It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.
In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art.